Adjustable resistor



July 18, 1950 M. E. BoURNs ADJUSTABLE REsIsToR 2 Sheets-Sheet l Filed Feb. 20. 1948 Alibi..

INVENTOR. MARLAN E. BOURNS BY A TTOR/VEV July 1s,- 1950 Filed Feb. 20, 1948 aa lr M, E. BOURNS ADJUSTABLE RESISTOR 2 Sheets-Sheet 2 76 gli@ INVENTOR.

MARLAN E BOI/RNS ATTORNEY Patented July 18, 1 950 UNITED STATES PATENT OFFICE 7 Claims.

This invention relates to adjustable resistors, and more particularly to adjustable resistors which must respond precisely and without ambiguity to the means which actuates the movable slider.

For many applications, particularly the detection and telemetering of conditions in and around a moving aircraft, it is essential that the detecting element be capable of being positioned accurately, precisely, and without lag in response to the condition to be observed.

It is an object of this invention to provide an adjustable resistor suited to be actuated by a detecting element as described immediately above.

It is another object of this invention to provide an adjustable resistor which will be rugged, reliable, simple in construction, and easily and accurately assembled.

It is another object of this invention to provide an adjustable resistor which may be subjected to accelerations up to 10 G without detrimental eiect to the instrument, and Without producing a false electric output.

It is another object of this invention to provide an adjustable resistor in which the electrical detection properties are very sensitive to the physical displacement of the mechanical arm and slider.

It is a further object of this invention to provide an adjustable resistor in which the actuating arm and slider may be moved by a very low actuating force.

It is a still further object of this invention to simplify adjustable resistor construction so that the instrument may be partially dismantled for installation and/or transportation and assembled without in the slightest altering the calibration of the instrument.

It is an additional object of this invention to provide an adjustable resistor in which the slider which rides on the adjustable resistor will not disengage from the element when the instrument is subjected to high acceleration and to severe vibration.

Another object of this invention is to simplify adjustable resistor construction so that need for special limit stops in the oscillatory path of the actuating arm is eliminated.

In accordance with these objects and with other objects which will become apparent in the following specification, the instant invention is embodied in a base, in which is movably mounted an actuating member or arm. Resilient contact means in the form of a resilient piece of conducting material is secured to the actuating member. A cover member is mounted on the base. Simplicity of construction is enhanced by fabricating the cover member of non-conducting material, and mounting on the inner face thereof a resistance element and a contact piece, the former engaging (when the cover is in place) a portion of the resilient contact means, the latter engaging another portion of the contact means. Thus, when the cover member is secured in place to the base, the resilient contact means is automatically engaged with the resistance element and with the contact piece at a proper, predetermined contact pressure.

Two embodiments of the invention described generally above have been illustrated in the drawings, wherein:

Figs. 1, 2, 3, and 4 illustrate a preferred embodiment, Fig. l being a plan View of the adjustable resistor with the cover partially broken away, Fig. 2 being a sectional elevation taken along line 2--2 in Fig. 1, Fig. 3 being a cross section taken along line 3--3 in Fig. 1, and Fig. 4 being a fragmentary section taken along line 4-4 in Fig. 2;

Fig. 5 is a diagrammatic sketch of the circuitry involved in the invention; and

Figs. 6, 7, 8, and 9 illustrate another embodi ment of the instant invention, Fig. 6 being an elevation partly sectionalized, Fig. '7 being a cross section taken along line 'l-l in Fig. 6, 8 being a view looking at the underside of the cover along the line 8-8 in Fig. 6, and Fig. 9 being a perspective view of one of the contact elements removed from the instrument.

First embodiment Referring to Figs. 1, 2, and 3, II designates a base having a recess I2 therein, partially closed by a wall I3 secured to the base lI by screws I4, and accurately positioned by dowel pins l5. EX- tending through the base II, the recess I2, and into the wall I3 is 2. shaft IS rotatably mounted therein by means of ball bearings l'l. Secured to the shaft I6 by any suitable means, such as a diametral pin I9, is an arm i@ made of nonconducting material. The arm I9 is thus oscillatable with respect to the base II by means of the shaft I6, the position of which is in turn conn trolled by a vane 2l, having formed on one end thereof a hub 22 bored at 23 to accept the external end of the shaft I6. The seating of a diametral pin 24 protruding from the shaft I6 in a pair of diametrically disposed V notches 26 in the hub 22 assures that the vane 2| will always be assembled in the proper predetermined relation with respect to the arm i9. A screw 2l extending through the end of the hub and threaded into the end of the shaft i6 serves to anchor the vane 2l to the shaft I6.

Near the end of the arm i9 opposite the shaft I6 there is secured, by means of screws 28, a resilient contact strip 29 of conducting material. The strip 29 is disposed generally parallel to the arm I9, and the two ends of the strip face outwardly of the recess I2, being terminated by button contact members 3l and 32, respectively.

Both elements with which the contact strip 29 engages are attached to the inner face of a nonconducting cover 33, which, in the final assembly, is secured to the base II over the recess I2 by screws 34. One of these elements, a wire Wound elongate resistance element 36, is disposed in an arcuate groove 31 formed on the inner face of the cover 33, and held thereto by means of terminal members .38, which extend through and are secured to the cover 33. The arcuate disposition of the groove 31 is adjacent the oscillatory path of the end 32 of the resilient strip 29, so that the strip 26 is constantly in contact with some portion of the resistance element 36 during all times that the cover 33 is in place. The element 36 is connected, both mechanically and electrically, at each end tothe respective terminals 38, by means of metallic strips 39, which are attached to the inner ends of the terminals 38 by the peening of the latter at 4I, and hooked over the element 36 at each end thereof as vshown at 42. The members 38 and 39 thus serve the double function of securing the element 36 to the inner face of the cover 33, and of providing electrical connections to each end thereof. The -terminal members 33 are drilled and tapped externally of the cover 33 to accommodate terminal screws 4-3, to which may be connected lead wires for the resistor.

The contact member 3 I on the other end of the resilient strip 28 is in constantcontact with a conducting piece or plate 44 held to the inner face ofthe cover 33 by a terminal member 46 passing through and secured in the cover 33. Like the terminal member v38, the member 46, which is peened over the surface of the plate l44 at 41, serves the double function of physically holding the plate 44 in place and of providing an electrica-l connection to the plate. The members 46 and 38 are splined, as exemplified at 48, to prevent turning. Member `46 is drilled and tapped externally of the cover Y33 to accommodate a terminal screw 49. A small screw 50 passing thru the plate 44 into the cover 33 prevents the Aplate from turning about the terminal member 46.

To minimize the effect of extraneous acceleration on the instrument and to further enhance its response characteristics, a counter-balance -screwA 5l is threaded into the arm I9 paral'leling the strip v29. Screw 5i has a knurled head '52 to 'aid in the 'balancing of the instrument while the arm I6 is mounted to the base -I i. A transverse set screw 53 threaded into the arm I-'9 serves to anchor the counter-balance screw 5i in place after adjustment.

Gross-balancing is effected by means of a screw 54 mounted in Aa tapped bore extending transversely through the arm I9 at a right angle to the shaft I6. After adjustment, the screw 54, which is generally positioned fully within its bore, is anchored in place by a set screw 56.

Low density material is employed for the vane 2'I to lower inertia, -thereby reducing lag in response, and minimizing the undesirable effects of acceleration. `The instrument is of manifest simplicity, being directly actuated without the employment of gears, links, or similar mechanisms. The frictional ltorque 'which the vane 2| must overcome is minimized by pivoting the shaft I6 in the ball bearings l1, by using low contact pressure -at vbutton-contacts 3l and `32, and by dis- Second embodiment In'the embodiment shown in Figs. 6, '1, 8, and 9, 6I represents a base having a groove therein formed .of two por-tions, a bore 62 and a slot 63 communicating with the top of the base 6I. A shaft 64 is reciprocably mounted in the bore A62, being prevented from rotation therein by a post 66 extending radially from the shaft 64 and through the groove 63 to a region above the base 6I. A contact plate 61 is secured to the top of the post 66 at a right angle thereto by a screw 68, and is insulated therefrom by a liber washer assembly 18. Each side of the plate is slotted and the resulting strips are bent upwardly to form .resilient -contacts 69 and 1I.

A cover 12 made of non-conducting material is secured to the base 6I over the groove 63, and carries an elongate resistance element "I3 and an elongate conducting .strip 14 seated in grooves 16 and 11, respectively, formed in the inner face of the cover 12. The element 13 is held in place by being secured at each end, as by soldering, to a pair of strips 8l, the opposite `ends of the strips 3| being held to the inner face of the cover 12 by Ythe terminals 82 which are peened over the strips 8l at 83. In a similar manner, the elongate strip 14 is held to the cover 12 by the strip 84 and the terminal 86.

Each of the terminals 82 and `86 is drilled and tapped Afor reception of terminal screws 81.

The end of the `base `6l opposite the mouth of the bore '62' is provided with a boss '88 through which extends a threaded mounting stud 89, 'by means of which the adjustable resistor may `be pivotally mounted to follow swinging movement of whatever driving means may be actuating shaft 64.

It will be noted that the groove 63 terminates short of the ends of the base 6i, so that the post 66 abutting the ends of the groove 63 limits reciprocation of the shaft 64. Screws 9i serve to secure vthe cover 12 tothe base 6I Like the first embodiment, shown in Figs, 1, -2

I and 3, the embodiment just described is also rugged, reliable, and simple in construction. Like the rst Vembodiment also VVthe insulating cover member carries `all the electrical terminals, yet is completely free of the actuating element, i. e., the shaft 64. Thus, the final assembly step, which is the simple placing of the cover '12 upon the base 3i, automatically veifectuates engagement between lthe two pairs of contact elements at a predetermined proper contact pressure.

An adjustable resistor constructed as vdescribed above has been found -to be able toelectrically-detect :a movement as small as 0.002 of an yinch of the'part of the shaft 64.

What is claimed is:

l. An adjustable resistor comprising a recessed base, a wal-l partially closing the recess in said base, a shaft rotatably mounted i-n said base and said wall and `spanning vsaid recess therebetween, a 4contro'l arm 'secured to said shaft between said Wall and said rbase and oscillatab-le thereby withv respect to said base, a contact strip secured intermediate its ends to said arm, a cover member` secured to said base, an arcuate resistance element mounted to the inner face of said cover member adjacent the path of movement of one end of said strip, an edge of said element pressing against said one end, and a contact plate secured to the inner face of said cover member adjacent the path of oscillation of the other end of said strip.

2. An adjustable resistor comprising a base, a shaft rotatably mounted in said base, a control arm secured to said shaft and oscillatable thereby With respect to said base, a wind vane secured to said shaft opposite said arm externally of said base effective to control position of said arm, a counter balance adjusting screw threaded into said arm opposite said shaft, a contact strip secured intermediate its ends to said arm, a cover member secured to said base, an arcuate resistance element mounted to the inner face of said cover member adjacent the path of movement of one end of said strip, an edge of said element pressing against said one end, and a contact plate, secured to the inner face of said cover member adjacent the path of oscillation of the other end of said strip.

3. An adjustable resistor comprising a base, a shaft rotatably mounted in said base, a control arm secured to said shaft and oscillatable thereby with respect to said base, a contact strip disposed generally parallel to said arm and secured intermediate its ends to said arm, a cover member secured to said base, an arcuate resistance element mounted to the inner face of said cover member adjacent the path of movement of the outer end of said strip, an edge of said element pressing against said outer end, a contact plate, a terminal passing through said cover member and securing said plate to the inner face of said cover member adjacent the path of oscillation of the inner end of said strip, and a pair of terminais passing thru said cover member at the respective ends of said element and attached to said element to secure the same to said base.

4. An adjustable resistor comprising a recessed base, a wall partially closing the recess in said base, a shaft rotatably mounted in said base and said wall and spanning said recess therebetween, a control arm secured to said shaft between said wall and said base and oscillatable thereby with respect to said base, a contact strip disposed generally parallel to said arm and secured intermediate its ends to said arm, a cover member secured to said base having an arcuate groove on its inner face adjacent the path of oscillation of the outer end of said strip, an arcuate resistance element mounted in said groove, an edge of said element pressing against said outer end, a contact plate, a terminal passing thru said cover member and securing said plate to the inner face of said cover member and securing said plate to the inner face of said cover member adjacent the path of oscillation of the inner end of said strip, and a pair of terminals passing thru said cover member at the respective ends of said element and attached to said element to secure the same in said groove.

5. An adjustable resistor comprising a recessed base, a shaft rotatably mounted in said base and extending into the recess, a control arm secured to said shaft and oscillatable thereby within said recess, a. wind vane secured to said shaft opposite said arm externally of said base effective to control position of said arm, a counter balance adjusting screw threaded into said arm opposite said shaft, a Contact strip disposed generally parallel to said arm and secured intermediate its ends to said arm, a cover member secured to said base having an arcuate groove on its inner face adjacent the path of oscillation oi the outer end of said strip, an arcuate resistance element mounted in said groove, an edge of said element pressing against said outer end, a contact plate, a terminal passing through said cover member and securing said plate to the inner face of said cover member adjacent the path of oscillation of the inner end of said strip, and a pair of terminals passing thru said cover member at the respective ends of said element and attached to said element to secure the same in said groove.

6. A vane controlled adjustable resistor comprising a base, a shaft extending therethru, a vane mounted on one end of said shaft, an arm mounted on the other end of said shaft extending diametrically of said vane, a counter-balance screw threaded radially into the end of said arm remote from said shaft having a head disposed externally of said arm, a set screw mounted to secure said counter-balance screw, said arm having a threaded bore transversely thereof, a crossbalance screw threaded within said bore, and a set screw mounted to secure said cross-balance screw.

7. An adjustable resistor comprising a base, a wall mounted parallel to and spaced from a portion of said base so that a recess exists therebetween, a shaft rotatably mounted in said base and said wall and spanning said recess therebetween, a control arm secured to said shaft between said wall and said base and oscillatable thereby with respect to said base, a cover member secured to said base, a contact strip secured to said arm, an arcuate resistance element mounted to the inner face of said cover member adjacent the path of movement of one end of said strip, an edge of said element pressing against said one end, and electrical return means forming an electrical path between said Contact strip and the exterior of said cover.

MARLAN E. BOURNS.

REFERENCES CITED The following references are of record in the le of this patent:

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